Arc tube



FIG. 1 is a front view of an arc tube of the present invention, wherein the rear view is a mirror image thereof;

FIG. 2 is a top view thereof, wherein the bottom view is a mirror image thereof; and,

FIG. 3 is a right side view, wherein the left side view is a mirror image thereof. 

We claim the ornamental design for an arc tube, as shown and described. 